GH Actions: harden the workflow against PHPCS ruleset errors

If there is a ruleset error, the `cs2pr` action doesn't receive an `xml` report and exits with a `0` error code, even though the PHPCS run failed (though not on CS errors, but on a ruleset error).

This changes the GH Actions workflow to allow for that situation and still fail the build in that case.

Author: jrfnl

.github/workflows/check-cs.yml

@@ -40,7 +40,9 @@ jobs:
         composer update --prefer-dist --no-suggest --no-progress --no-interaction
 
     - name: Check Code Style
+      id: phpcs
       run: vendor/bin/phpcs --report-full --report-checkstyle=./phpcs-report.xml
 
     - name: Show PHPCS results in PR
+      if: ${{ always() && steps.phpcs.outcome == 'failure' }}
       run: cs2pr ./phpcs-report.xml